The distribution of water in the early Cretaceous lithospheric mantle of the North China Craton and implications for its destruction
The distribution of water in the early Cretaceous lithospheric mantle of the North China Craton and implications for its destruction
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DOI：
10.1016/j.lithos.2020.105412
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发表时间：
2020-05
期刊：
影响因子：
3.5
通讯作者：
Zi-Zhen Wang;Jia Liu;Q. Xia;Yan-Tao Hao;Qin-Yan Wang
中科院分区：
文献类型：
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作者：
Zi-Zhen Wang;Jia Liu;Q. Xia;Yan-Tao Hao;Qin-Yan Wang
有人认为，地幔柱的寿命部分与其深部地幔根的低含水量有关，这导致其粘度比下面的软流圈高得多。因此，岩石圈根的去除被认为与最低岩石圈地幔的水化作用密切相关。华北克拉通（NCC）通常被认为是这种“破坏克拉通”的代表，但以往的含水量调查主要集中在NCC东部的边缘地区，这意味着内部地区的水化状态仍然不清楚。在这里，我们提出了全岩地球化学和Sr-Nd-Pb同位素数据的早白垩世基性岩体在内部的NCC东部，并计算其相应的原生熔体的水含量。我们还估计了产生这些熔体的岩石圈地幔的水含量。基性岩具有弧形不相容微量元素特征和富集Sr-Nd同位素组成。单斜辉石斑晶的水含量，通过傅立叶变换红外光谱法（FTIR）测定，从37到472 ppm。相应的原生熔体的水含量，这是使用单斜辉石水含量和单斜辉石/熔体分配系数的水计算，范围从0.85至2.07重量%。地幔源区的含水量估计至少为571-1214 ppm，远高于卡普瓦尔橄榄岩捕虏体的含水量（<10 ppm）。结合新的数据与以前的结果，我们表明，最低的岩石圈地幔下的东部NCC在其边缘和内部地区的水化在早白垩世，这强调了水的作用在岩石圈地幔变薄。
It has been suggested that the longevity of cratons is related in part to the low water content of their deep mantle roots, which leads to a much higher viscosity than that of the underlying asthenosphere. Consequently, removal of cratonic roots is thought to be closely related to hydration of the lowermost lithospheric mantle. The North China Craton (NCC) is generally considered to represent such a “destroyed craton”, but previous investigations of the water content have focused mainly on the marginal areas of the eastern part of the NCC, meaning that the state of hydration in the interior region remains unclear. Here, we present whole-rock geochemical and Sr-Nd-Pb isotope data for the early Cretaceous mafic intrusions in the interior of the eastern part of the NCC and calculate the water contents of their corresponding primary melts. We also estimate the water contents of the lithosphere mantle that produced these melts. The mafic rocks exhibit arc-like incompatible-trace-element signatures and enriched Sr-Nd isotopic compositions. The water contents of clinopyroxene phenocrysts, as measured by Fourier transform infrared spectrometry (FTIR), vary from 37 to 472 ppm. The water contents of the corresponding primary melts, which were calculated using the clinopyroxene water contents and the clinopyroxene/melt partitioning coefficient of water, range from 0.85 to 2.07 wt%. The estimated water contents of the mantle source are at least 571-1214 ppm and are considerably higher than the H2O contents (<10 ppm) of Kaapvaal peridotite xenoliths. Combining the new data with previous results, we show that the lowermost lithospheric mantle beneath the eastern part of the NCC in both its marginal and interior regions was hydrated during the early Cretaceous, which underlines the role of water in the thinning of the lithospheric mantle.